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Abstract

Porcine circovirus 2 (PCV2) is a virus with a single-stranded, DNA circular genome that is ubiquitous in pig populations worldwide. PCV2 is the causative agent of the post-weaning multisystemic wasting syndrome (PMWS), a multifactorial disease that affects six to twelve-week-old pigs, and which is characterized by weight loss and immunosuppression. PCV2 vaccination has diminished the presentation of PMWS in the field, although PCV2 infection is not prevented.
PCV2 infects lymphocytes and it depends on the host enzymes to replicate. Enhanced PCV2 infection rates are associated with increased mitotic activity, although the effect of PCV2 replication on lymphoid cell function is unknown. The main goal of this thesis was to understand the interactions of PCV2 with the swine immune system, by determining the effect of PCV2 on the antibody response in pigs under field conditions, and studying the impact of the primary PCV2 infection on lymphocyte activation, proliferation, and viability. As shown in Chapter 2, a PCV2 persistent infection was detected in farmed pigs of all age groups. Furthermore, a great variability in their neutralizing antibody titers was observed, regardless of their vaccination status. Chapter 3 provides details about the establishment of an in vitro cell model to study the effect of primary PCV2 infection on the immune cells, by using snatched-farrowed, porcine colostrum deprived (SF-pCD) PCV2-free pigs as blood donors of PCV2-naïve peripheral blood mononuclear cells (PBMCs). These cells were exposed to the polyclonal mitogens ionomycin/PMA and PCV2 infection. As shown in chapters 4 & 5, enhanced PCV2 infection rates in ionomycin/PMA-stimulated PBMCs, decreased proliferation in PCV2 infected cells, and high bystander cell death rates in PCV2-exposed PBMCs were observed. This thesis contributes to the current knowledge on PCV2 immunology by bringing insight into factors that contribute to viral pathogenesis and immune modulation and emphasizes the need of developing new vaccines that prevent PCV2 infection.